The invention relates to a heat exchanger of the type including banks or registers of double-pipe elements attached at opposite ends thereof to oval headers which are provided bilaterally with transition elements welded to main headers and forming a transition from the oval cross section to a round cross section.
Heat exchangers of this type are employed for the rapid cooling of hot process gases, high-pressure steam being simultaneously produced. The essential elements of such heat exchangers are the double pipes comprising concentrically arranged inner and outer pipes and the oval headers welded to the pipe ends. In this manner there are formed banks or registers of pipe elements that are arranged in parallel to one another and joined to the main headers of the heat exchanger.
As is well known, the hot process gases flow through the inner pipes of the banks, while the cooling water flows through the annular gap between the inner and outer pipes. The oval headers feed the cooling water to one end of the pipe element. At the other end of the pipe element, the oval headers lead the resultant produced mixture of steam and water off to the main headers.
The double-pipe arrangement provides the advantage that all pressure-leading components can be made to have a low wall thickness even for use with high steam pressures. Thus, local excessive thermal stresses will not be formed in the system. The differences in expansion between the heated inner pipes and the outer pipes subjected to the temperature of saturated steam are compensated due to the high elasticity of the arrangement.
The oval headers as such are welded together in a gas tight manner in the longitudinal direction, so as to form components comparable to tube plates having a low wall thickness even at high pressures.
The oval headers are produced from deformation of round pipes and are provided with transition elements that form the transition from the oval cross section to a round cross section, so as to permit welding of the oval headers to the main headers. Under the deformation processes hitherto employed for the manufacture of the oval headers, i.e. such as warm rolling on dual rolls in the form of shape rolls or cold rolling on a bending roll, it was necessary to make the transition elements as separate components that were then welded to the oval headers. However, such a weld is difficult to achieve due to its shape or form. Accordingly, the manufacture of known oval headers has been very complex and expensive, and includes the substantial danger of leaks formed in the welds.